We usually associate solar hot water with panels and a collector tank installed on a roof. Heat pumps use different technology to a solar hot water system.
How does a heat pump work?
A heat pump is similar technology to a reverse Cycle Air Conditioner. It transfers the heat in the air to the water stored inside the heater through a heat exchange system. In the case of heat pumps, “heat” is a relative term as they will still work in very cold conditions – as low as 3 degrees Celsius, so it will still be generating hot water for you during winter nights. How is that possible?
External air is drawn into the heat pump system via a fan into an evaporator, containing a special type of refrigerant. This CFC free refrigerant has an evaporation or boiling point of -26C, whereas water has a boiling point of 100C. Temperatures that feel very cold to us are still more than enough to make the refrigerant “boil”. The air that has been drawn into the system, which is far warmer than the refrigerant, turns the refrigerant from a liquid into a gas inside the heat pump’s piping. A compressor then pumps the now gaseous refrigerant through a small valve, which compresses it and as a result of the process generates a great deal of heat. A heat exchanger transfers the heat from the heated refrigerant gas pipes to a tank where water is stored. The temperature of the refrigerant has now dropped dramatically as the heat has been drawn away, so it returns to a liquid state and the heat pump cycle begins again.